Gidday,
I know from my enquiries that it is near impossible to get a Floscan out of
Floscan! The only suitable model is called a 264PB-15 and if you tell them
it is for a plane, forget it. So, don't tell them that, but it seems this
range is very limited and mostly sold to the likes of Blue Mountains, and
Rocky Mountains Instruments.
Reg
Tony Renshaw
Sydney Australia
Read this to hopefully clarify:
Fluctuating Fuel Flow Indications:
My Grand Rapids EIS-4000 engine monitor (which uses the standard FloScan
201 fuel flow transducer) has indicated fluctuating fuel flow since I began
using it (40 hours total on aircraft). In flight (or when running the
engine on the ground), I'd see flow rates that vary by up to +- 0.5 gph in
just a few seconds. (I have an O-360 A1A, carbeurated). My fuel system is:
tank - filter - L/R valve - floscan - Facet pump - gascolator - engine fuel
pump - carb. Grand Rapids was happy to send me a new floscan transducer,
but it didn't help, nor did moving the transducer to a location between the
gascolator and the engine fuel pump.
In addition, when the Facet fuel pump was on, the indicated flow rate
jumped up at least 1 gph.
I spent the weekend trying different transducer locations, then I called
FloScan on Monday (FloScan provides transducers to most of the fuel flow
and engine monitor manufacturers). It turns out the diaphram pump on the
engine (and the Facet pump) produce pulses that travel back down the fuel
tube to the FloScan transducer's turbine. The pulses cause the turbine to
momentarily stutter or turn back just a bit. This causes the FloScan to
generate more pulses than it should, indicating an incorrectly high fuel
flow. The random interaction between the pulses and the normal fuel flow
caused my fluctuating flow rate indications.
FloScan recommended two possible solutions. Rather than using the 201
transducer, they make a 264 transducer, with an internal dampening
diaphram. But they won't sell to individuals, just avionics companies. The
other alternative is a pulse absorber, which is just a 1.5" metal sphere
inserted in the fuel line between the transducer and the fuel pump(s). Air
trapped in the sphere compresses when the pulses come along, absorbing the
pulses so they don't screw up the transducer. They won't sell the sphere
for aviation use, however, only for boats. Instead of the $30 metal sphere,
I tried a $3 Fram G-3 fuel filter. It's about 1.5" diameter, comes with
3/8" ID hose to mate with -6 aluminum fuel lines, and is transparent (so
you can be sure there is air trapped in the filter housing).
Problem solved. When flying in level flight, the fuel flow indication is
now steady. When I turn on the fuel pump the flow rate initially surges as
the pump pulls fuel from the filter, but the flow rate then returns to
normal as the flow stabilizes.
Another problem licked!
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